Shift register

ABSTRACT

A shift register is disclosed, which can prevent malfunctioning of device by decreasing the load on a discharging voltage source line, and can decrease a size of stage. The shift register comprises a plurality of stages to sequentially output scan pulses through respective output terminals, wherein each of the stages comprises a pull-up switching unit controlled based on a signal state of node, and connected between the output terminal and any one among a plurality of clock transmission lines to transmit the clock pulses provided with sequential phase differences; and a node controller to control the signal state of node, and to discharge the node by using the clock pulse from any one among the plurality of clock transmission line.

The present patent document is a divisional of U.S. patent applicationSer. No. 13/187,984, filed Jul. 21, 2011 and U.S. Pat. No. 8,041,488,filed Dec. 28, 2007, which claims priority to Korean Patent ApplicationNo. 10-2007-0023835 filed in Korea on Mar. 12, 2007.

BACKGROUND

1. Field of the Invention

The present invention relates to a shift register of a liquid crystaldisplay (LCD) device, and more particularly, to a shift register whichcan prevent malfunctioning of device by decreasing load on a dischargingvoltage source line and can decrease a size of stage.

2. Discussion of the Related Art

In general, a liquid crystal display (LCD) device displays images bycontrolling light transmittance of liquid crystal with the use of anelectric field applied. For this, the LCD device is provided with aliquid crystal panel including a plurality of pixel regions arranged ina matrix configuration, and a driving circuit for driving the liquidcrystal panel.

The liquid crystal panel comprises a plurality of gate lines and aplurality of data lines, wherein each gate line is formed orthogonal toeach data line, to thereby define a plurality of pixel regions. Inaddition, the liquid crystal panel includes pixel electrodes and acommon electrode to apply the electric field to the pixel regions,respectively. At this time, the gate lines are driven in response to ascan pulse generated from a shift register, in sequence.

FIG. 1 is a diagram illustrating one stage in a related art shiftregister. As shown in FIG. 1, the related art shift register includes aplurality of stages 100. The stages 100 are cascaded. Each stage issupplied with a clock pulse from a clock transmission line, and outputsthe scan pulse in sequence. Each stage includes a plurality of nodes; anode controller to control a signal state of the node; and an outputunit, connected to the node, to output the scan pulse in response to thesignal state of the node. In order to maintain the node as a dischargingstate, the related art shift register uses a discharging voltage sourcecorresponding to a constant voltage.

However, the related art shift register has the following disadvantages.

When the discharging voltage source is supplied to the node controllerand output unit included in each stage, there is large load on adischarging voltage source line for transmitting the discharging voltagesource. The related art shift register has may malfunction since thenode included in each stage is not discharged properly.

Also, the related art stage is provided with at least two nodes and aplurality of switching devices to control the nodes, so that the shiftregister is increased in size. This large size of shift register maycause the limitation on technology of forming the shift register in theliquid crystal panel.

BRIEF SUMMARY

A shift register comprises a plurality of stages to sequentially outputscan pulses through respective output terminals. Each of the stagescomprises a pull-up switching unit controlled based on a signal state ofnode, and connected between the output terminal and any one among aplurality of clock transmission lines to transmit the clock pulsesprovided with sequential phase differences. A node controller controlsthe signal state of node, and discharges the node by using the clockpulse from any one among the plurality of clock transmission line.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram illustrating one stage included in a related artshift register;

FIG. 2 is a diagram illustrating a shift register according to thepreferred embodiment of the present disclosure;

FIG. 3 is a timing diagram illustrating various signals supplied to oroutput from each stage of FIG. 2;

FIG. 4 is a diagram illustrating a first circuit structure of stage ofFIG. 2;

FIG. 5 is a diagram illustrating a second circuit structure of stage ofFIG. 2;

FIG. 6 is a diagram illustrating a third circuit structure of stage ofFIG. 2;

FIG. 7 is a diagram illustrating a fourth circuit structure of stage ofFIG. 2;

FIG. 8 is a diagram illustrating a fifth circuit structure of stage ofFIG. 2;

FIG. 9 is a diagram illustrating a sixth circuit structure of stage ofFIG. 2;

FIG. 10 is a diagram illustrating a seventh circuit structure of stageof FIG. 2;

FIG. 11 is a diagram illustrating an eighth circuit structure of stageof FIG. 2;

FIG. 12 is a diagram illustrating a ninth circuit structure of stage ofFIG. 2;

FIG. 13 is a diagram illustrating a tenth circuit structure of stage ofFIG. 2;

FIG. 14 is a diagram illustrating a circuit structure of first to thirdstages of FIG. 2; and

FIG. 15 is a waveform diagram illustrating a scan pulse from a seventhstage included in a shift register having a circuit structure of FIG.14.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Hereinafter, a shift register according to the preferred embodiments ofthe present disclosure will be described with reference to theaccompanying drawings.

As shown in FIG. 2, a shift register according to the preferredembodiment of the present disclosure includes ‘n’ stages ST1 to STn anda dummy stages (not shown). Each of the stages ST1 to STn outputs a scanpulse Vout1 to Voutn for one frame period, wherein the scan pulses aresequentially output from the first stage ST1 to the dummy stages.

The scan pulses Vout1 to Voutn output from the respective stages ST1 toSTn except the dummy stages are sequentially supplied to gate linesincluded in a liquid crystal panel (not shown), thereby scanning thegate lines in sequence. Sequentially, the first stage ST1 outputs thefirst scan pulse Vout1, the second stage ST2 outputs the second scanpulse Vout2, the third stage ST3 outputs the third scan pulse Vout3, . .. , the ‘n’th stage STn outputs the ‘n’th scan pulse Voutn finally.

After the ‘n’th stage STn outputs the ‘n’th scan pulse Voutn, first andsecond dummy stages output the scan pulses. Then, the scan pulse outputfrom the first dummy stage is supplied to the ‘n−1’th stage. Also, thescan pulse output from the second dummy stage is supplied to the ‘n’thstage STn. This shift register is formed in the liquid crystal panel.That is, the liquid crystal panel includes a display area to displayimages, and a non-display area surroundings the display area. The shiftregister is formed in the non-display area.

All stages ST1 to STn and dummy stages included in the shift registerare supplied with a charging voltage source VDD, a discharging voltagesource VSS charging voltage source VDD and the discharging voltagesource VSS correspond to D.C. voltages sources, wherein the chargingvoltage source VDD has a positive polarity, and the discharging voltagesource VSS has a negative polarity. The discharging voltage source VSSmay be a grounded voltage.

The clock pulses may use two or more clock pulses. The shift registeraccording to the present invention uses the six clock pulses, that is,first to sixth clock pulses CLK1 to CLK6. The first to sixth clockpulses CLK1 to CLK6 are output with the sequential phase differences.The sequential output from the first to sixth clock pulses CLK1 to CLK6is performed repeatedly. That is, after completing the sequential outputfrom the first clock pulse CLK1 to the sixth clock pulse CLK6, the firstto sixth clock pulses CLK1 to CLK6 are sequentially output again.

Based on the circuit structure of the stage, the number of clock pulsessupplied to one stage may be variable. Among the stages ST1 to STn+1,the first stage ST1 positioned uppermost is supplied with a start pulseVst as well as the charging voltage source VDD, the discharging voltagesource VSS, and the first to sixth clock pulses CLK1 to CLK6. For oneframe period, the clock pulses CLK1 to CLK6 are output several times.However, the start pulse Vst is output once for one frame period. Inother words, the respective clock pulses CLK1 to CLK6 periodicallyrepresent the active state (high state) several times for one frameperiod, but the start pulse Vst represents the active state once for oneframe period. At this time, the sixth clock pulse CLK6 may be output insynchronization with the start pulse Vst. Among the first to sixth clockpulses CLK1 to CLK6, the sixth clock pulse CLK6 is output firstly.

As shown in FIG. 3, the start pulse Vst and the first to sixth clockpulses CLK1 to CLK6 may have the high states which are partiallyoverlapped for a predetermined period at the same time. Although notshown, it is possible to output the start pulse and the first to sixthclock pulses CLK1 to CLK6 without being overlapped to one another.

To make each of the stages ST1 to STn output the scan pulse, it isnecessary to precede an enable operation for each of the stages ST1 toSTn. Enabling the stage, that is, being the stage of output-enable statecorresponds to the state of that the stage is set to output the clockpulse supplied thereto as the scan pulse. For this, each of the stagesST1 to STn is supplied with the scan pulse from the previous stagethereof, whereby each of the stages ST1 to STn is enabled. For example,the ‘k’th stage is enabled in response to the scan pulse from the‘k−2’th stage.

There is no stage being positioned one row ahead of the first stage ST1positioned uppermost, and two rows ahead of the second stage ST2. Thefirst and second stages ST1 and ST2 are enabled in response to the startpulse Vst from a timing controller. Also, each of the stages ST1 to STnis disabled in response to the scan pulse from the next stage thereof.Disabling the stage, that is, being the stage of output-disable statecorresponds to the state of that the stage is reset not to output theclock pulse supplied thereto as the scan pulse. For example, the ‘k’thstage is disabled in response to the scan pulse from the ‘k+2’th stage.

The detailed explanation for each of the stages ST1 to STn included inthe shift register according to the present disclosure will be describedas follows.

FIG. 4 is a diagram illustrating a first circuit structure of stage ofFIG. 2. As shown in FIG. 4, each of the stages ST1 to STn and dummystages is comprised of a node n, a node controller NC, a pull-up switchTrpu, and a first pull-down switch Trpd1.

The node controller NC controls a signal state of the node n. That is,the node controller NC makes the node n charged or discharged.Especially, the node controller NC uses the clock pulse instead of thedischarging voltage source VSS when the node controller NC makes thenode N discharged.

The pull-up switch Trpu is turned-on when the node n is charged. Afterthat, when the pull-up switch Trpu is turned-on, the pull-up switch Trpuoutputs the clock pulse supplied thereto. The clock pulse output fromthe turned-on pull-up switch Trpu corresponds to the scan pulse. Thepull-up switch Trpu included in the stages ST1 to STn and dummy stagesoutputs the scan pulse in response to the charging voltage source VDDcharged in the node n, and supplies the scan pulse to the correspondinggate line, the next stage and the previous stage through an outputterminal 340.

In more detail, the pull-up switch Trpu included in the ‘k’th stageoutputs the scan pulse in response to the charging voltage source VDDcharged in the node of the ‘k’th stage, and supplies the scan pulse tothe ‘k’th gate line, the ‘k+2’th stage and the ‘k−2’th stage. For this,a gate terminal of the pull-up switch Trpu is connected to the node n; adrain terminal thereof is connected to a clock transmission line; and asource terminal thereof is connected to the output terminal 340 of the‘k’th stage. At this time, the output terminal 340 of the ‘k’th stage isconnected to the ‘k’th gate line, the ‘k+2’th stage and the ‘k−2’thstage. For example, the pull-up switch Trpu included in the third stageST3 outputs the third clock pulse CLK3 as the third scan pulse Vout3,and supplies the third clock pulse CLK3 to the third gate line, thefifth stage ST5 and the first stage ST1.

In response to the clock pulse, the first pull-down switch Trpd1 isturned-on. Then, the first pull-down switch Trpd1 being turned-onoutputs the discharging voltage source VSS supplied thereto. The firstpull-down switch Trpd1 included in each of the stages ST1 to STn anddummy stages outputs the discharging voltage source VSS in response tothe clock pulse, and supplies the discharging voltage source VSS to thecorresponding gate line, the previous stage and the next stage.

In more detail, the first pull-down switch Trpd1 included in the ‘k’thstage outputs the discharging voltage source VSS in response to theclock pulse, and supplies the discharging voltage source VSS to the‘k’th gate line, the ‘k+2’th stage and the ‘k−2’th stage. For this, thefirst pull-down switch Trpd1 has a gate terminal connected to a clocktransmission line, a source terminal connected to a discharging voltagesource transmission line, and a drain terminal connected to the outputterminal 340 of the ‘k’th stage. At this time, the output terminal 340of the ‘k’th stage is connected to the ‘k’th gate line, the ‘k+2’thstage and the ‘k−2’th stage. For example, the first pull-down switchTrpd1 included in the third stage ST3 outputs the discharging voltagesource VSS in response to the fifth clock pulse CLK5, and supplies thedischarging voltage source VSS to the third gate line GL3, the fifthstage ST5 and the first stage ST1. The gate line is charged by the scanpulse output from the pull-up switch Trpu, and is discharged by thedischarging voltage source VSS output from the first pull-down switchTrpd1.

The detailed structure for the node controller NC will be explained asfollows. The node controller NC includes first and second switchingunits Tr1 and Tr2.

The first switching unit Tr1 included in each of the stages ST1 to STnand dummy stages responds to the scan pulse from the previous stage, andsupplies the charging voltage source VDD to the node n of the currentstage. In more detail, the first switching unit Tr1 included in the nodecontroller NC of the ‘k’th stage responds to the ‘k−2’th scan pulseoutput from the ‘k−2’th stage, and supplies the charging voltage sourceVDD to the node n of the ‘k’th stage. For this, the first switching unitTr1 of the ‘k’th stage includes the gate terminal connected to theoutput terminal 340 of the ‘k−2’th stage, the drain terminal connectedto the charging voltage source transmission line, and the sourceterminal connected to the node n of the ‘k’th stage. For example, thefirst switching unit Tr1 included in the third stage ST3 charges thenode n of the third stage ST3 by the charging voltage source VDD inresponse to the first scan pulse Vout1 from the first stage ST1.

The second switching unit Tr2 included in each of the stages ST1 to STnand dummy stages responds to the scan pulse from the next stage, andsupplies the clock pulse to the node n of the current stage. In moredetail, the second switching unit Tr2 included in the node controller NCof the ‘k’th stage responds to the ‘k+2’th scan pulse from the ‘k+2’thstage, and supplies the clock pulse to the node n of the ‘k’th stage.For this, the second switching unit Tr2 included in the ‘k’th stageincludes the gate terminal connected to the output terminal 340 of the‘k+2’th stage; the source terminal connected to the clock pulsetransmission line; and the drain terminal connected to the node n of the‘k’th stage.

The clock pulse supplied to the drain terminal of the second switchingunit Tr2 included in the ‘k’th stage is identical to the clock pulsesupplied to the drain terminal of the pull-up switch Trpu included inthe ‘k’th stage.

The scan pulse supplied to the gate terminal of the second switchingunit Tr2 included in the ‘k’th stage is synchronized with the clockpulse supplied to the gate terminal of the first pull-down switch Trpd1included in the ‘k’th stage. Accordingly, the first pull-down switchTrpd1 and the second switching unit Tr2 included in the ‘k’th stage areturned-on at the same time.

The second switching unit Tr2 corresponds to the switching unit fordischarging the node n. The second switching unit Tr2 discharges thenode n by using the clock pulse instead of the related art dischargingvoltage source VSS.

The clock pulse is synchronized with the period of turning-on the secondswitching unit Tr2, whereby the clock pulse is maintained as anon-active state, that is, low state. Meanwhile, the clock pulse ismaintained as a high state at a following period (output period of thestage) just after the pull-up switch Trpu is turned-on. Thus, the stagesST1 to STn and dummy stages can output the scan pulse for the outputperiod by using the pull-up switch Trpu and the clock pulse of highstate, and also discharge the node n for the disable period by using thesecond switching unit Tr2 and the clock pulse of low state. For example,the second switching unit Tr2 included in the third stage ST3 dischargesthe node n of the third stage ST3 by the third clock pulse CLK3 of lowstate in response to the fifth scan pulse Vout5 from the fifth stageST5. As shown in FIG. 3, the third clock pulse CLK3 is maintained as thelow state for the period of outputting the fifth scan pulse Vout5.

FIG. 5 is a diagram illustrating a second circuit structure of stage ofFIG. 2. The second circuit structure of FIG. 5 is similar to the firstcircuit structure of FIG. 4. In case of the second circuit structure ofFIG. 5, the drain terminal of the first pull-down switch Trpd1 isconnected to the clock transmission line instead of the dischargingvoltage source transmission line.

At this time, the drain terminal of the first pull-down switch Trpd1,the drain terminal of the pull-up switch Trpu, and the drain terminal ofthe second switching unit Tr2 are connected to the same clocktransmission line, and are also supplied with the same clock pulse. Forexample, the third clock pulse CLK3 is supplied to the drain terminal ofthe first pull-down switch Trpd1, the drain terminal of the secondswitching unit Tr2 and the drain terminal of the pull-up switch Trpuincluded in the third stage ST3.

In the second circuit structure, the first pull-down switch Trpd1discharges the output terminal 340 at the disable period of dischargingthe node n according as the second switching unit Tr2 is turned-on. Atthis time, the second switching unit Tr2 discharges the output terminal340 by using the clock pulse of low state instead of the dischargingvoltage source VSS.

In case of the second circuit structure of FIG. 5, the dischargingvoltage source VSS is not used in the output unit (including the pull-upswitch Trpu and first pull-down switch Trpd1) as well as the nodecontroller NC. This second circuit structure of FIG. 5 can reduce theload on the discharging voltage source transmission line as comparedwith that of the first circuit structure.

FIG. 6 is a diagram illustrating a third circuit structure of stage ofFIG. 2. The third circuit structure of FIG. 6 is similar to the firstcircuit structure of FIG. 4. In case of the third circuit structure ofFIG. 6, the drain terminal of the first pull-down switch Trpd1 isconnected to the clock transmission line instead of the dischargingvoltage source transmission line, and the gate terminal of the firstpull-down switch Trpd1 is connected to the output terminal 340 insteadof the clock transmission line. At this time, the drain terminal of thefirst pull-down switch Trpd1, the drain terminal of the pull-up switchTrpu, and the drain terminal of the second switching unit Tr2 areconnected to the same clock transmission line, and are also suppliedwith the same clock pulse.

The first pull-down switch Trpd1 is maintained in the turning-off stateat a moment of supplying the clock pulse of high state to the outputterminal 340 according as the pull-up switch Trpu is turned-on, wherebyit has no effect on the output period of stage. That is, if the clockpulse of high state is supplied to the output terminal 340, thepull-down switch Trpd functions as an inverted-direction diode. However,the first pull-down switch Trpd1 is turned-on when the clock pulse oflow state supplied to the drain terminal of the first pull-down switchTrpd falls to the low state. The first pull-down switch Trpd1 beingturned-on supplies the clock pulse of low state to the output terminal340, thereby discharging the output terminal 340.

FIG. 7 is a diagram illustrating a fourth circuit structure of stage ofFIG. 2. The fourth circuit structure of FIG. 7 is similar to the firstcircuit structure of FIG. 4. The node controller NC included in thefourth circuit structure of FIG. 7 additionally includes a thirdswitching unit Tr3 as well as the first and second switching units Tr1and Tr2 included in the first circuit structure of FIG. 4.

Each of the stages ST1 to STn and dummy stages includes the thirdswitching unit Tr3, wherein the third switching unit Tr3 included ineach of the stages ST1 to STn and dummy stages supplies the scan pulsefrom the previous stage to the node n of the current stage in responseto the clock pulse. In more detail, the third switching unit Tr3included in the node controller NC of the ‘k’th stage supplies the‘k−1’th scan pulse from the ‘k−1’th stage to the node n of the ‘k’thstage in response to the clock pulse. For this, the third switching unitTr3 included in the ‘k’th stage includes the gate terminal connected tothe clock transmission line, the drain terminal connected to the outputterminal 340 of the ‘k−1’th stage, and the source terminal connected tothe node n of the ‘k’th stage. For example, the third switching unit Tr3included in the third stage ST3 charges the node n of the third stageST3 by the second scan pulse Vout2 in response to the second clock pulseCLK2.

In the meantime, the third switching unit Tr3 included in the nodecontroller NC of the ‘k’th stage may supply the ‘k−2’th scan pulse fromthe ‘k−2’th stage to the node n of the ‘k’th stage in response to theclock pulse. For this, the gate terminal of the second switching unitTr2 included in the ‘k’th stage is connected to the clock transmissionline; the drain terminal thereof is connected to the output terminal 340of the ‘k−2’th stage; and the source terminal thereof is connected tothe node n of the ‘k’th stage. For example, the third switching unit Tr3included in the third stage ST3 charges the node n of the third stageST3 by the first scan pulse Vout1 in response to the first clock pulseCLK1. In this case, the clock pulse supplied to the gate terminal of thethird switching unit Tr3 included in the ‘k’th stage is synchronizedwith the scan pulse supplied to the gate terminal of the first switchingunit Tr1 included in the ‘k’th stage. Accordingly, the first switchingunit Tr1 and the third switching unit Tr3 included in the ‘k’th stageare turned-on at the same time.

FIG. 8 is a diagram illustrating a fifth circuit structure of stage ofFIG. 2. The fifth circuit structure of FIG. 8 is similar to the secondcircuit structure of FIG. 5. However, the node controller NC of thefifth circuit structure of FIG. 8 additionally includes a thirdswitching unit Tr3 as well as the first and second switching units Tr1and Tr2 included in the second circuit structure of FIG. 5. The thirdswitching unit Tr3 of FIG. 8 is identical to the aforementioned thirdswitching unit Tr3 of FIG. 7, whereby the detailed explanation for thethird switching unit Tr3 is omitted.

FIG. 9 is a diagram illustrating a sixth circuit structure of stage ofFIG. 2. The sixth circuit structure of FIG. 9 is similar to the thirdcircuit structure of FIG. 6. However, the node controller NC included inthe sixth circuit structure of FIG. 9 additionally includes a thirdswitching unit Tr3 as well as the first and second switching units Tr1and Tr2 included in the third circuit structure of FIG. 6.

FIG. 10 is a diagram illustrating a seventh circuit structure of stageof FIG. 2. The seventh circuit structure of FIG. 10 is similar to thefourth circuit structure of FIG. 7. However, the node controller NCincluded in the seventh circuit structure of FIG. 10 additionallyincludes a fourth switching unit Tr4 as well as the first to thirdswitching units Tr1 to Tr3 included in the fourth circuit structure ofFIG. 7.

Each of the stages ST1 to STn and dummy stages includes the fourthswitching unit Tr4, wherein the fourth switching unit included in eachof the stages ST1 to STn and dummy stages supplies the dischargingvoltage source VSS to the node n of the current stage. In more detail,the fourth switching unit Tr4 included in the node controller NC of the‘k’th stage supplies the discharging voltage source VSS to the node n ofthe ‘k’th stage in response to the start pulse Vst. For this, the gateterminal of the fourth switching unit Tr4 included in the ‘k’th stage isconnected to the start pulse transmission line for transmitting thestart pulse; the drain terminal thereof is connected to the node n ofthe ‘k’th stage; and the source terminal is connected to the dischargingvoltage source transmission line.

The fourth switching unit Tr4 may be included in each for all thestages, or may be included in each for the other stages except thestages being enabled by the start pulse. That is, the fourth switchingunit Tr4 is not formed in each of the first and second stages ST1 andST2 enabled by the start pulse Vst.

If the fourth switching unit Tr4 is provided in each for all the stages,the drain terminal of the fourth switching unit Tr4 included in thestages enabled by the start pulse Vst is supplied with the followingcontrol signal instead of the discharging voltage source VSS. Thecontrol signal is maintained as the active state (that is, high state)for the period of turning-on the fourth switching unit Tr4, and ismaintained as the non-active state (that is, low state) for the periodof turning-off the fourth switching unit Tr4. The control signal may beprovided in an inverted shape at an angle of 180° with respect to thestart pulse Vst.

The stages including the fourth switching unit Tr4 among the otherstages except the stage enabled by the start pulse Vst are disabled atthe same time in response to the start pulse Vst. For example, thefourth switching unit Tr4 included in the third stage ST3 discharges thenode n of the third stage ST3 by the discharging voltage source VSS inresponse to the start pulse Vst.

FIG. 11 is a diagram illustrating an eighth circuit structure of stageof FIG. 2. The eighth circuit structure of FIG. 11 is similar to thefifth circuit structure of FIG. 8. However, the node controller NCincluded in the eighth circuit structure of FIG. 11 additionallyincludes a fourth switching unit Tr4 as well as the first to thirdswitching units Tr1 to Tr3 included in the fifth circuit structure ofFIG. 8. The fourth switching unit Tr4 of FIG. 11 is identical to thefourth switching unit Tr4 of FIG. 10, whereby the detailed explanationfor the fourth switching unit Tr4 is omitted.

FIG. 12 is a diagram illustrating a ninth circuit structure of stage ofFIG. 2. The ninth circuit structure of FIG. 12 is similar to the sixthcircuit structure of FIG. 10. However, the node controller NC includedin the ninth circuit structure of FIG. 12 additionally includes a fourthswitching unit Tr4 as well as the first to third switching units Tr1 toTr3 included in the sixth circuit structure of FIG. 10. The fourthswitching unit Tr4 of FIG. 12 is identical to the fourth switching unitTr4 of FIG. 10, whereby the detailed explanation for the fourthswitching unit Tr4 is omitted.

FIG. 13 is a diagram illustrating a tenth circuit structure of stage ofFIG. 2. The tenth circuit structure of FIG. 13 is similar to the ninthcircuit structure of FIG. 12. However, the node controller NC includedin the tenth circuit structure of FIG. 13 additionally includes a secondpull-down switch Trpd2 as well as the first pull-down switch Trpd1included in the ninth circuit structure of FIG. 10.

The second pull-down switch Trpd2 is included in each of the stages ST1to STn and dummy stages. The second pull-down switch Trpd2 included inthe current stage outputs the clock pulse of low state in response tothe scan pulse from the next stage, and supplies the clock pulse of lowstate to the corresponding gate line, the previous stage and the nextstage through the output terminal 340. In more detail, the secondpull-down switch Trpd2 included in the ‘k’th stage outputs the clockpulse of low state in response to the ‘k+2’th scan pulse from the‘k+2’th stage, and supplies the clock pulse of low state to the ‘k’thgate line, the ‘k+2’th stage and the ‘k−2’th stage. For this, the gateterminal of the second pull-down switch Trpd2 is connected to the outputterminal 340 of the ‘k+2’th stage; the drain terminal thereof isconnected to the clock transmission line; and the source terminalthereof is connected to the output terminal 340 of the ‘k’th stage. Atthis time, the output terminal 340 of the ‘k’th stage is connected tothe ‘k’th gate line, the ‘k+2’th stage and the ‘k−2’th stage.

At this time, the drain terminal of the second switching unit Tr2, thedrain terminal of the pull-up switch Trpu, the drain terminal of thefirst pull-down switch Trpd1, and the drain terminal of the secondpull-down switch Trpd2 are connected to the same clock transmissionline, and are also supplied with the same clock pulse. For example, thedrain terminal of the second switching unit Tr2, the drain terminal ofthe pull-up switch Trpu, the drain terminal of the first pull-downswitch Trpd1, and the drain terminal of the second pull-down switchTrpd2 included in the third stage ST3 are supplied with the third clockpulse CLK3.

The second pull-down switch Trpd2 included in the tenth circuitstructure discharges the output terminal 340 for the disable period ofdischarging the node n according as the second switching unit Tr2 isturned-on. At this time, the second pull-down switch Trpd2 dischargesthe output terminal 340 by using the clock pulse of low state instead ofusing the discharging voltage source VSS.

In each of the circuit structures, the first switching unit Tr1 of thecurrent stage is turned-on by the scan pulse from the previous stage, tothereby supply the scan pulse from the previous stage to the node n. Forexample, the first switching unit Tr1 included in the ‘k’th stage isturned-on by the ‘k−2’th scan pulse from the ‘k−2’th stage, so that the‘k−2’th scan pulse is supplied to the node n, thereby charging the noden. Also, the ‘k’th stage is enabled by the ‘k−1’th scan pulse from the‘k−1’th stage, instead of the ‘k−2’th scan pulse from the ‘k−2’th stage.In this case, the gate terminal of the first switching unit Tr1 includedin the ‘k’th stage is supplied with the ‘k−1’th scan pulse from the‘k−1’th stage.

In FIGS. 4, 5, 7, 8, 10 and 11, the kind of clock pulse supplied to thegate terminal of the first pull-down switch Trpd1 varies insynchronization with the scan pulse based on which stage outputs thescan pulse supplied to the gate terminal of the second switching unitTr2. For example, if the gate terminal of the second switching unit Tr2included in the third stage ST3 of FIG. 4 is supplied with the fourthscan pulse Vout4 from the fourth stage ST4, the gate terminal of thefirst pull-down switch Trpd1 is supplied with the fourth clock pulseCLK4 synchronized with the fourth scan pulse Vout4.

An operation of the shift register according to the present inventionwill be explained as follows.

FIG. 14 is a diagram illustrating a circuit structure of first to thirdstages of FIG. 2. At this time, the first to third stages of FIG. 14include the ninth circuit structure of FIG. 12. The first and secondstages ST1 and ST2 of FIG. 14 are enabled by the start pulse Vst,wherein the first and second stages ST1 and ST2 has the circuitstructure from which the fourth switching unit Tr4 is removed. Also, thethird stage ST3 includes the fourth switching unit Tr4.

First, an initial period T0 will be explained as follows. For theinitial period T0, as shown in FIG. 3, only start pulse Vst ismaintained as the high state, and the first to sixth clock pulses CLK1to CLK6 are maintained as the low state. The start pulse Vst is input toall stages including the first to third stages ST1 to ST3.

In detail, the start pulse Vst is supplied to the drain terminal of thethird switching unit Tr3 and the gate terminal of the first switchingunit Tr1 included in the first stage ST1. Then, the first switching unitTr1 of the first stage ST1 is turned-on. Through the first switchingunit Tr1 being turned-on, the start pulse Vst of high state is suppliedto the node n of the first stage ST1. Accordingly, the node n of thefirst stage ST1 is charged by the start pulse Vst of high state, and thepull-up switch Trpu whose gate terminal is connected to the charged noden is turned-on. Meanwhile, there is no output from the third stage ST3for the initial period TO, whereby the second switching unit Tr2 of thefirst stage ST1 is turned-off.

An operation of the second stage ST2 for the initial period TO will beexplained as follows. The start pulse Vst is supplied to the secondstage. In detail, the start pulse Vst is supplied to the gate terminalof the first switching unit Tr1 included in the second stage. Thus, thefirst switching unit Tr1 is turned-on. Through the turned-on firstswitching unit Tr1, the charging voltage source VDD is supplied to thenode n of the second stage ST2. Accordingly, the node n is charged bythe charging voltage source VDD, and the pull-up switch Trpu whose gateterminal is connected to the charged node n is turned-on.

An operation of the third stage ST3 for the initial period TO will beexplained as follows. The start pulse Vst of high state output for theinitial period TO is supplied to the gate terminal of the fourthswitching unit Tr4 included in the third stage ST3. Then, the fourthswitching unit Tr4 of the third stage ST3 is turned-on. Through theturned-on fourth switching unit Tr4, the discharging voltage source VSSis supplied to the node n of the third stage ST3. Accordingly, the noden of the third stage ST3 is discharged by the discharging voltage sourceVSS, and the pull-up switching unit Trpu whose gate terminal isconnected to the discharged node n is turned-off. Meanwhile, there is nooutput from the fifth stage ST5 for the initial period T0, whereby thesecond switching unit Tr2 of the fifth stage ST5 is turned-off. For theinitial period T0, the fourth to ‘n’th stages ST4 to STn and the dummystages are operated in the same mode as that of the third stage ST3.

A first period T1 will be explained as follows.

For the first period T1, as shown in FIG. 3, the start pulse Vst and thefirst clock pulse CLK1 are maintained as the high state, and the secondto sixth clock pulses CLK2 to CLK6 are maintained as the low state.Accordingly, the other stages as well as the first to third stages ST1to ST3 and the dummy stages repeat once the operation for the initialperiod T0 by the start pulse Vst of high state, and the followingoperation is performed by the first clock pulse CLK1 of the high state.That is, since the start pulse Vst is maintained as the high state forthe first period T1, the first switching unit Tr1 included in the firststage ST1 is turned-on. Thus, the node n of the first stage ST1 ischarged for the first period T1. As a result, the pull-up switch Trpuwhose gate terminal is connected to the charged node n is alsoturned-on.

As the first clock pulse CLK1 of high state is supplied to the drainterminal of the first pull-up switch Trpu being turned-on, the pull-upswitch Trpu outputs the first clock pulse CLK1 of high state as thefirst scan pulse Vout1 for the first period T1, and supplies the firstscan pulse Vout1 to the first gate line, the second stage ST2 and thethird stage ST3 through the output terminal 340. According as the firstclock pulse CLK1 of the high state is supplied to the output terminal340 of the first stage ST1, the first clock pulse CLK1 of high state issupplied to the gate terminal, the drain terminal and the sourceterminal included in the first pull-down switch Trpd1. As a result, thefirst pull-down switch Trpd1 is maintained in the turning-off state.

The first scan pulse Vout1 is supplied to the drain terminal of thethird switching unit Tr3 included in the second stage ST2. Also, thefirst clock pulse CLK1 of the high state is supplied to the gateterminal of the third switching unit Tr3 included in the second stageST2. Accordingly, the third switching unit Tr3 is turned-on. Then, thefirst scan pulse Vout1 of the high state is supplied to the node n ofthe second stage ST2 through the third switching unit Tr3 beingturned-on. Accordingly, the pull-up switch Trpu of the second stage ST2whose gate terminal is connected to the charged node n is turned-on.

Also, the first scan pulse Vout1 is supplied to the gate terminal of thefirst switching unit Tr1 included in the third stage ST3. Then, thefirst switching unit Tr1 of the third stage ST1 is turned-on.Accordingly, the charging voltage source VDD is supplied to the node nof the third stage ST3 through the first switching unit Tr1 beingturned-on. Even though the discharging voltage source VSS is supplied tothe node n of the third stage ST3 through the turned-on fourth switchingunit Tr4 for the first period, the node n of the third stage ismaintained in the charged state by the charging voltage source VDD.Accordingly, the pull-up switch Trpu whose gate terminal is connected tothe charged node n is turned-on.

Meanwhile, since the second to sixth clock pulses CLK2 to CLK6 are inthe low state for the first period T1, there is no output from the otherstages. In brief, for the first period T1, the first stage ST1 outputsthe first scan pulse Vout1, and the second and third stages ST2 and ST3are enabled.

An operation for a second period T2 will be explained as follows.

For the second period T2, as shown in FIG. 3, the first and second clockpulses CLK1 and CLK2 are maintained as the high state, and the startpulse and the third to sixth clock pulses CLK3 to CLK6 are maintained asthe low state. In response to the start pulse Vst of the low state, thefirst switching unit Tr1 of the first stage ST1 is turned-off. Inresponse to the sixth clock pulse CLK6 of the low state, the thirdswitching unit Tr3 of the first stage ST1 is turned-off.

According as the first and third switching unit Tr1 and Tr3 areturned-off, the node n of the first stage ST1 is maintained as afloating state. Thus, the node n of the first stage ST1 is maintained asthe charged state by the charging voltage source VDD applied for theinitial period T0. As a result, the pull-up switch Trpu of the firststage ST1 whose gate terminal is connected to the node n is maintainedin the turning-on state. At this time, the first clock pulse CLK1 issupplied to the pull-up switch Trpu being turned-on. Then, the chargingvoltage source VDD charged in the node n of the first stage ST1 isamplified (bootstrapping).

Accordingly, the first clock pulse CLK1 supplied to the drain terminalof the pull-up switch Trpu included in the first stage ST1 is stablyoutput through the source terminal of the pull-up switch Trpu. The firstclock pulse CLK1 output from the pull-up switch Trpu corresponds to thefirst scan pulse Vout1. For the second period T2, the first stage ST1outputs the first scan pulse Vout1 which is maintained as a perfecttarget voltage.

Also, the second clock pulse CLK2 maintained as the high state for thesecond period T2 is supplied to the second stage ST2. That is, thesecond clock pulse CLK2 is supplied to the drain terminal of the secondswitching unit Tr2, the drain terminal of the pull-up switch Trpd1, andthe drain terminal of the first pull-down switch Trpd1 included in thesecond stage ST2. The second clock pulse CLK2 supplied to the secondstage ST2 is output to the output terminal 340 of the second stage ST2through the pull-up switch Trpu being turned-on.

The second clock pulse CLK2 output through the pull-up switch Trpucorresponds to the second scan pulse Vout2. This second scan pulse Vout2is supplied to the second gate line, the third stage ST3 and the fourthstage ST4. The second scan pulse Vout2 supplied to the third stage ST3enables the third stage, and the second scan pulse Vout2 supplied to thefourth stage ST4 enables the fourth stage ST4. In brief, the first stageST1 outputs the first scan pulse Vout1 which reaches the perfect targetvoltage for the second period T2; the second stage ST2 starts to outputthe second scan pulse Vout2; and the third and fourth stages ST3 and ST4are enabled.

An operation for a third period T3 will be explained as follows.

For the third period T3, as shown in FIG. 3, the second and third clockpulses CLK2 and CLK3 are maintained as the high state. Meanwhile, thestart pulse Vst, the first clock pulse CLK1, and the fourth to sixthclock pulses CLK4 to CLK6 are maintained as the low state. For the thirdperiod T3, the second stage ST2 outputs the second scan pulse Vout2which reaches the perfect target voltage; the third stage ST3 starts tooutput the third scan pulse Vout3; and the fourth and fifth stages ST4and ST5 are enabled. Also, for the third period T3, the third scan pulseVout3 output from the third stage ST3 is supplied to the first stageST1, whereby the first stage ST1 is disabled.

This disable operation will be explained in detail as follows.

That is, the third scan pulse Vout3 from the third stage ST3 is suppliedto the gate terminal of the second switching unit Tr2 included in thefirst stage ST1. Accordingly, the second switching unit Tr2 isturned-on. Through the second switching unit Tr2 being turned-on, thefirst clock pulse CLK1 of the low state is supplied to the node n of thefirst stage ST1. Thus, the node n of the first stage ST1 is dischargedby the first clock pulse CLK1 of the low state.

For the third period T3, the first pull-down switch Trpd1 included inthe first stage ST1 is turned-on since the first clock pulse CLK1 of thelow state is supplied to the drain terminal of the first pull-downswitch Trpd1. The first pull-down switch Trpd1 being turned-on suppliesthe first clock pulse CLK1 of the low state to the output terminal 340of the first stage ST1, so that it is possible to prevent the leakage ofvoltage in the first gate line for the non-output period of the firststage ST1.

In this same method, the second stage ST2 discharges its node n by usingthe second clock pulse CLK2 of the low state in response to the fourthscan pulse Vout4 from the fourth stage ST4. The other stages dischargetheir nodes n by the clock pulse for the non-output period, according tothe same method aforementioned.

FIG. 15 is a waveform diagram illustrating a scan pulse from a seventhstage included in a shift register having a circuit structure of FIG.14. As shown in FIG. 15, the voltages of node and scan pulse are stablyoutput.

As mentioned above, the shift register according to the presentinvention has the following advantages.

First, the node is discharged by using the clock pulse instead of thedischarging voltage source, so that it is possible to decrease the loadon the discharging voltage source transmission line.

According as the nodes and switching devices are decreased in number,the stage is also decreased in size.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. The shift register of claim 1, wherein the first switching unitincluded in the node controller of the ‘n’th stage is controlled by thescan pulse from the ‘n−1’th stage or the scan pulse from the ‘n−2’thstage; and the second switching unit included in the node controller ofthe ‘n’th stage is controlled by the scan pulse from the ‘n+2’th stageor the scan pulse from the ‘n+3’th stage.
 2. The shift register of claim1, wherein the current stage includes a first pull-down switch which iscontrolled by the clock pulse from any one among the plurality of clocktransmission lines, and is connected between the output terminal and thedischarging voltage source transmission line to transmit the dischargingvoltage source, and the first pull-down switch and the second switchingunit are turned-on at the same period.
 3. The shift register of 2,wherein the node controller of the current stage includes a thirdswitching unit which is controlled by the clock pulse from any one amongthe plurality of clock transmission lines, and is connected between thenode and the output terminal of the previous stage, and the clock pulsesupplied to the third switching unit and the scan pulse supplied to theoutput terminal of the previous stage have the same phase.
 4. The shiftregister of claim 3, wherein the node controller of the current stageincludes a fourth switching unit which is controlled by a first controlsignal having an active state once for one frame period, and isconnected between the node and a control signal transmission line totransmit a second control signal, and the second control signalcorresponds to a signal whose phase is inverted by 180° with respect tothe first control signal.
 5. The shift register of claim 1, wherein thecurrent stage includes a first pull-down switch which is controlled bythe clock pulse from any one among the plurality of clock transmissionlines, and is connected between the output terminal and any one amongthe plurality of clock transmission lines, wherein the first pull-downswitch and the second switching unit are turned-on at the same period,and the source or drain terminal of the first pull-down switch, thesecond switching unit and the pull-up switch are connected to the sameclock transmission line.
 6. The shift register of claim 5, wherein thenode controller of the current stage includes a third switching unitwhich is controlled by the clock pulse from any one among the pluralityof clock transmission line and is connected between the node and theoutput terminal of the previous stage, and the clock pulse supplied tothe third switching unit and the scan pulse supplied to the outputterminal of the previous stage have the same phase.
 7. The shiftregister of claim 6, wherein the node controller of the current stageincludes a fourth switching unit which is controlled by a first controlsignal having an active state once for one frame period, and isconnected between the node and a control signal transmission line totransmit a second control signal, and the second control signalcorresponds to the discharging voltage source or a signal whose phase isinverted by 180° with respect to the first control signal.
 8. The shiftregister of claim 4 wherein the first control signal corresponds to astart pulse.
 9. The shift register of claim 4 wherein the first controlsignal corresponds to a start pulse, and any one of the clock pulses issynchronized with the start pulse.
 10. The shift register of claim 3wherein the node controller provided for each of the other stages exceptthe stage enabled by the start pulse includes a fourth switching whichis controlled by the first control signal having the active state oncefor one frame period, and is connected between the node and the chargingvoltage source line.
 11. The shift register of claim 1, wherein the nodecontroller included in the stage enabled by the start pulse includes: afirst switching unit which is controlled by the start pulse and isconnected between the node and a start pulse transmission line totransmit the start pulse; and a second switching unit which iscontrolled by the scan pulse from the next stage and is connectedbetween the node and any one of the clock transmission lines, whereinthe second switching unit is turned-on for a period of a non-activestate in the clock pulse of the clock transmission line connected to thesecond switching unit, and the second switching unit and the pull-upswitch are connected to the same clock transmission line.
 12. The shiftregister of claim 4 wherein the second control signal corresponds to asignal whose phase is inverted by 180° with respect to the first controlsignal, and the second control signal is supplied to the drain or drainterminal of the first switching unit.